1. Field of the Invention
The present invention relates to an image recording material having an image formed (recorded) by an image-forming device in an electrophotographic system and an image display material using said image recording material.
2. Description of the Related Art
As image-forming techniques have been developed in recent years, methods of forming images of similar qualitiy inexpensively in large amounts by various printing methods such as intaglio printing, letterpress printing, planographic printing, gravure printing and screen printing are known. In particular, screen-printing can highly accurately produce printed materials (commodities) of highly sophisticated design, such as displays or membrane switches for household appliances, various labels, the clock faces, outdoor signboards, posters and scarves. It is assumed that these printed materials are used not only in ordinary indoor environments (office environments) but also outdoors, and thus there is demand for high heat resistance at a temperature of about 100xc2x0 C. and high light resistance to sunlight (mainly UV rays). Accordingly, when printed materials to be used outdoors are formed by screen printing, a pigment-based ink excellent in heat resistance and light resistance so as not to deteriorate the qualities of images at a temperature of about 100xc2x0 C. for several hundreds hours or in a light resistance testing machine such as a sunshine meter or a fade meter for several hundreds hours is selected and used, in consideration of the fact that the printed materials are to be used under UV rays or sunrays.
Screen printing requires many printing plates in accordance with the number of images to be printed, and color printing requires additional printing plates in accordance with the number of colors. In particular, printed materials of highly sophisticated design are required often in a small number of different forms (production of a small number of different kinds of printed materials) so that the printing plates must be remade every time shapes of the pointed materials change, or the printing plates are changed to cope with a different number of printed materials, thus requiring a large number of different kinds of printing plates. Accordingly, the production of printed materials of highly sophisticated design by screen printing has a problem, in that storage and handling of a large number of printing plates require a lot of trouble and time.
In the screen printing process, organic solvents and the like are contained in the ink, so that not only the influence of the organic soluvents on the human body but also environmental pollution should be taken into consideration. Further, drying of these organic solvents requires enormous energy and time for drying, and causes a reduction in productivity. In order to utilize the printing plate repeatedly, the printing plate must be washed, thus requiring a large amount of organic solvents for the washing. When the printing plate is replaced, a screen printing head stained with previously-used ink should also be replaced, and cleaning the head requires time, leading to a further reduction in productivity.
On the other hand, formation (printing) of an image in the electrophotographic system is conducted by charging an image carrier uniformly and exposing it to light in accordance with an image signal, to form an electrostatic latent image by a potential difference between an exposed portion and a non-exposed portion, followed by electrostatic development of a color powder (image forming material) called a toner having polarity opposite to the charge thereby forming a visuable image (toner image). In the case of a color image, this process is repeatedly carried out to form visual color images which are then transferred and fixed (mainly by cooling the previously thermally melted color powder), to obtain a color image.
As described above, the electrostatic latent image on the image carrier is electrically formed using an image signal in the electrophotographic system, thus permitting not only the same image to be repeatedly formed but also different image to be easily formed. Further, the toner image on the image carrier can be transferred almost completely to the image recording material, and the slight amount of toner image remaining on the image carrier can be easily removed by a resin blade or a brush, and thus printed materials can be produced easily in a small number of different forms.
The toner is formed typically by mixing additives such as hot-melt resin, a pigment, and, if necessary, a charge controlling agent, and pulverizing the mixture through milling. As compared with the pulverized toner, the electrostatic latent image in the electrophotographic system has sufficiently high resolution, and can be expected to have sufficiently high resolution, even compared to screen printing.
Further, the color toner has four primary colors of cyan, magenta, yellow and black, and by mixing these colors, any color identical to those in printing can be theoretically obtained. Further, the color toner can be arbitrarily blended with a toner resin and a pigment, and thus the shielding of an image by the toner can be easily increased. Further, when a small number of required colors are required, single-color toners can be layered for further increasing the shielding of the image.
It is assumed that the image-recording material (printing paper) of the electrophotographic system will be used in the general office environment, that is, at a temperature of 10xc2x0 C. to 30xc2x0 C. under about 15% to 85% humidity, and therefore, there has been almost no examination of heat resistance and light, which resistance assumes that the image-recording material will be used outdoors. In the formation of a color image in the electrophotographic system, however, pigments of cyan, magenta, yellow and black, which have excellent light resistance are being used, so the image recording material in the electrophotographic system can be expected to be highly light resistant. When a heat-resistant toner is selected, it is thought that the image recording material can also be endowed with heat resistance to such an extent as to be usable outdoors.
As compared with silk screening, the formation of an image with the electrophotographic system requires no planographic plate as described above, and different, vivid images can be easily produced. Therefore, the image recording material in the electrophotographic system is used under various situations. recent topics in the medical field are a name card (with a photograph of a face), which is used for confirmation of a medical worker, and a display material, which has a photograph of a face and is recently being attached to a bed of a hospitalized patient in order to identify the patient, thus preventing mistakes in treatment. The displaying material using a printing paper can be easily forged, easily damaged and easily combusted, and therefore, printing of the display material on a film or plate is desired. Moreover, in consideration of pathogenic microorganisms in the hospital, such as MRSA, there is also a demand for imparting the display material with functions such as microbial resistance and flame retardancy. Further, when the surface of the indicating material is glossy like a photographic paper, the surface thereof may be poor in visibility because of light reflection depending on the viewing angle. Accordingly, it is also desired that the gloss of the surface be suppressed to improve visibility.
In the electrophotographic system, however, when an image-forming substrate is made of a thin film, an image cannot follow flexing of the film when a sufficient amount of a toner is fixed as the image. This causes a problem such as cracking on the surface of the image. In the electrophotographic system, fixing temperature and fixing pressure are sufficiently applied by a fixing roller at the time of fixation process, and thus the toner is sufficiently melted to obtain a high-gloss (color) image having a flat surface. The high-gloss color image gives excellent image qualities in the case of a photographic image of relatively high density, while a considerable difference in gloss between the high-gloss color image and the surface of the printing paper causes problems such as remarkable xe2x80x9cglitteringxe2x80x9d and a deterioration in visibility attributable to a change in gloss depending on the viewing angle as described above.
To prevent a reduction in the visibility of an image depending on the viewing direction, a method has been proposed, in which a toner having a high melting temperature is used in the electromagnetic system, and the toner is fixed under such conditions as not to be sufficiently melted, thus reducing the surface gloss of the image. However, when the toner is not sufficiently melted, a part of the toner is often melted unevenly, resulting not only in uneven gloss (phenomenon of partially varying gloss) but also in a deterioration in fixation of the toner to the image recording material, so controlling surface gloss by the fixing conditions is difficult.
Further, Japanese Patent Application Laid-Open (JP-A) No. 9-171266 proposes an image recording material and a method of controlling the surface gloss of an image wherein a porous coating solution consisting of a porous resin is applied onto an image-receiving layer, to form a porous film on the surface of the image-receiving layer thereby increasing surface scattering and reducing the surface gloss, and simultaneously a toner is embedded in this porous coating thereby reducing the surface gloss of the image. However, it is difficult to reduce the surface gloss sufficiently with this method, and a sufficient amount of a toner is necessary for raising the shielding power of the image, and thus an excess of the toner which cannot be adsorbed onto the porous coating may increase the surface gloss of the image.
Further, a method of reducing surface gloss by making a surface uneven by techniques such as sand blasting to reduce surface gloss by light scattering on the surface has also been proposed. However, sand blasting should be conducted vigorously in order to increase uniformity of the surface, resulting in problems such as the surface gloss being overly reduced and a reduction in image qualities due to the uneven surface of the image.
A phenomenon of fusion of a color toner with a fixing roller (hot offset) is known to occur when a color image is formed by the electrophotographic system. To prevent this phenomenon, the fixing roller is dipped in, coated with, or provided with, a release agent such as silicone oil, but a great problem arises in the fixing device; that is, the writing ability of an image is deteriorated due to adhesion of the silicone oil to the image recording material, the adhesion of an adhesive tape to the image recording material is made insufficient, the texture of the recording material is deteriorated due to stickiness, qualities of the image such as transmittance are deteriorated, and the abrasion resistance of the roll is lowered due to dipping in the oil.
As a counter measure to these related problems, a method of fixing without using an oil (oil-less fixing) and a method of using a toner (oil-less toner) comprising a toner resin blended with various release agents such as an organic polymer wax such as polyethylene wax and polypropylene wax or natural wax such as carnauba wax, have been proposed in order to prevent offset.
Under the presence circumstances, however, there is a problem, in that, for the purpose of forming an excellent image and improving the ability of the image to be stored, a color coating paper or a color-image OHP film provided on the surface of a substrate with an image-receiving layer having high affinity for a toner cannot be subjected to fixation without using a fixing oil because the whole surface of the image recording material is contacted with the fixing roll, resulting in the offset of the image recording material on the fixing roll.
As described above, when the image-forming surface is to be endowed with gloss or other functions required for use in severe environments, regulation of the functions is difficult for the reason unique to the image in the electrophotographic system. This is also a problem when other various functions are given to the image-forming surface.
The present invention is made to solve the problem described above, and an object of the invention is to provide an image recording material and an image display material using the same, which-are capable of easily forming a high-quality image with good visibility and have sufficient heat resistance, light resistance and flame retardancy even in outdoor use. Another object of the invention is to provide an image-recording material and an image display material using the same, which have functions capable of coping with various environments. Still another object of the invention is to provide an image-recording material and an image display material using the same, which do not generate the phenomenon of offset even if an oil-less toner is used.
To achieve these objects, as a result of extensive studies, the inventors discovered an image recording material having a structure wherein an image-receiving layer is disposed on one side of a transparent substrate, and a reverse image (mirror image) is formed such that when the image is viewed through the substrate, the image is seen as a normal rotation image (normal image) on the surface of the image-receiving layer, while the other side of the substrate is provided with a regulation-controlling means having various functions such as regulation of gloss.
That is, a first aspect of the present invention is an image recording material comprising: a transparent substrate; an image-receiving layer for forming an image by an electrophotographic system and disposed on one side of the substrate; and a function-controlling means disposed on the other side of the substrate;
wherein the image-receiving layer include a polyester resin which comprises a structural unit represented by the structural formula (I) and which has a number average molecular weight of 12,000 to 45,000: 
wherein n and m represent integers such that a molar ratio n/m is from 1 to 9.
A second aspect of the present invention provides the image recording material, wherein the image-receiving layer further comprises a charge controlling agent.
A third aspect of the present invention provides the image recording material, wherein the charge controlling agent is a surfactant.
A fourth aspect of the present invention provides the image recording material, wherein the function controlling means comprises a function-controlling layer for controlling at least one function selected from gloss, microbial resistance, flame retardancy, light resistance and chargeability.
A fifth aspect of the present invention provides the image recording material, wherein the function-controlling layer has a function of controlling gloss, and the function-controlling layer comprises a resin and a filler.
A sixth aspect of the present invention provides the image recording material, wherein the function-controlling layer has a function of controlling microbial resistance, and the function-controlling layer comprises an inorganic antimicrobial agent.
A seventh aspect of the present invention provides the image recording material, wherein the function-controlling layer has a function of controlling light resistance, and the function-controlling layer comprises at least one of an UV absorber and an antioxidant.
A eighth aspect of the present invention provides the image recording material, wherein a protective layer is disposed on the surface of the image-receiving layer.
A ninth aspect of the present invention provides a protective film comprising at least a transparent substrate, an image-receiving layer for forming an image by an electrophotographic system are disposed on one side of the substrate, and a function controlling means disposed on the other side of the substrate,
wherein the image-receiving layer include a polyester resin which comprises a structural unit represented by the structural formula (I) and which has a number average molecular weight of 12,000 to 45,000: 
wherein n and m represent integers such that a molar ratio n/m is from 1 to 9.
A tenth aspect of the present invention provides the protective film, wherein the image-receiving layer further comprises a charge controlling agent.
A eleventh aspect of the present invention provides the protective film, wherein the charge controlling agent is a surfactant.
A twelfth aspect of the present invention provides the protective film, wherein the function controlling means comprises a function-controlling layer for controlling at least one function selected from gloss, microbial resistance, flame retardancy, light resistance and chargeability.
A thirteenth aspect of the present invention provides the protective film, wherein the function-controlling layer has a function of controlling gloss, and the function-controlling layer comprises a resin and a filler.
A fourteenth aspect of the present invention provides the protective film, wherein the function-controlling layer has a function of controlling microbial resistance, and the function-controlling layer comprises an inorganic antimicrobial agent.
A fifteenth aspect of the present invention provides the protective film, wherein the function-controlling layer has a function of controlling light resistance, and the function-controlling layer comprises at least one of a UV absorber and an antioxidant.
A sixteenth aspect of the present invention provides the protective film, wherein a protective layer is disposed on the surface of the image-receiving layer.
A seventeenth aspect of the present invention provides the image display material comprising at least a transparent substrate, an image-receiving layer for forming an image by an electrophotographic system are disposed on one side of the substrate, and a function controlling means disposed on the other side of the substrate,
wherein the image-receiving layer include a polyester resin which comprises a structural unit represented by the structural formula (I) and which has a number average molecular weight of 12,000 to 45,000: 
wherein n and m represent integers such that a molar ratio n/m is from 1 to 9.